Prosthesis

ABSTRACT

Osteoarthritis (OA) is the most common disease affecting human joints. Mechanical stress through the joint is one of the most important independent etiological factors. The present invention provides a prosthesis that by passes some of the stress from the joint without destroying the joint surface. It allows may provide a full range of joint movement, while sharing the load with the physiological joint, thereby maintaining the viability of the physiological joint surface. In addition, the prosthesis can accommodate native soft tissue structures in or around the joint, such as ligaments.

STATEMENT OF CORRESPONDING APPLICATIONS

The present application is a Continuation of U.S. Non-Provisional patentapplication Ser. No. 15/355,807, filed Nov. 18, 2016; which is aContinuation-in-Part of U.S. Non-Provisional patent application Ser. No.13/514,239, filed Jun. 6, 2012; which is a U.S. National Stageapplication under 35 USC 371 of PCT Application Serial No.PCT/NZ2010/000211, filed on Oct. 21, 2010; which claims priority fromU.S. Provisional Patent Application No. 61/253,907, filed Oct. 22, 2009;the entirety of each of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a prosthetic device which is surgicallyimplantable into a body joint to support the joint.

BACKGROUND ART

Osteoarthritis (OA) is the most common disease affecting human joints.It is second only to cardiovascular disease as the cause of chronicdisability in adults. Worldwide, billions of dollars are spent annuallyfor its treatment and for the lost days in work.

OA is widely considered to be a degenerative joint disease and more than50% of individuals above the age of 65 years have clinical evidence ofOA. Nevertheless, OA cannot be described as a simple consequence ofaging. Epidemiological studies have shown a strong correlation of OAwith obesity, physical sports and occupation. Moreover, mechanicalstress through the joint has been suggested as one of the most importantindependent etiological factors.

While physiological stress is needed for cartilage and bone sustenanceand repair, excessive stress through joint surface leads to initiationand progression of OA. Prolonged high stress and excessive impulsivestress are detrimental to cartilage viability, whereas repetitivephysiological stress is beneficial for cartilage health.

Patients with OA generally present with pain, stiffness and deformity ofthe joint. Present treatment protocols are mainly symptomatic treatment.Initial management of most patients includes changes in lifestyle,Non-Steroidal Anti-Inflammatory Drugs (NSAIDs), analgesics, physicaltherapy, bracing and ambulatory aids. Surgical treatment is indicatedonly when consecutive treatment fails to improve the symptoms.

With particular reference to the knee common surgical options includearthroscopic debridement, high tibial osteotomy (HTO), andunicompartmental or tricompartmental knee replacement. In general,present forms of joint replacement surgery completely sacrifice thenatural joint and only provide limited symptom relief and restrictedmobility. Further, the lifespan of the replaced joint is also limited.None of the presently available treatment methods change the naturalprogress of the disease.

It is known to provide knee implants. One example of such a device isdisclosed in United States Patent Publication No. 2008/0275561 A1 toExploramed NC4, Inc. The patent discloses various implants used forabsorbing energy between body parts, and in particular knee joints.

The implants disclosed in the Exploramed patent are intended to absorbenergy when the knee is extended (e.g. the leg is straight). That energyis absorbed by an energy manipulator such as a spring or elastomericmaterial. The energy is subsequently distributed into the localised kneearea on flexion of the knee (e.g. bending of the leg). However, theconfigurations of the implants of the Exploramed patent only rely on thenative knee joint to provide the range of motion for knee movement. Thatis, the ends of the tibia and femur bones continue to providearticulation of the knee. This limits effectiveness of the discloseddevices as it will affect the natural mechanism of the knee joint suchas by creating an unnatural arc of motion.

An implant must also be positioned inside the body e.g. inside oradjacent to a joint. However, the implant may interact with parts of thejoint such as the ligaments which hold the bones of the joint together.For instance, an implant could lie overtop of, or otherwise rub, theligaments, and/or could restrict the ligaments as the joint movesthrough a native range of motion. This is a particularly difficult issueto address because the ligaments around the knee are complex, and theshape, orientation and direction of these change as the knee flexes.These issues can reduce or limit the effectiveness of the implant(s), orits suitability for use in treating certain conditions.

It is an object of the present invention to provide an improved implantand method of employing same.

It is also an object of the invention to provide an implant which may bemore easily implanted to a patient.

It is yet a further object of the invention to provide an implant whichmay reduce or minimise the adverse effects on the native knee joint whenimplanted therein.

Yet a further object of the invention is to provide an implant whichreduces undesirable interactions with ligaments and muscles forming partof, or adjacent to, a joint.

In addition, it is an object of the present invention to address theforegoing problems or at least to provide the public and medicalprofession with a useful choice.

In this specification where reference has been made to patentspecifications, other external documents, or other sources ofinformation, this is generally for the purpose of providing a contextfor discussing the features of the invention. Unless specifically statedotherwise, reference to such external documents is not to be construedas an admission that such documents, or such sources of information, inany jurisdiction, are prior art, or form part of the common generalknowledge in the art.

All references, including any patents or patent applications cited inthis specification are hereby incorporated by reference. No admission ismade that any reference constitutes prior art. The discussion of thereferences states what their authors assert, and the applicants reservethe right to challenge the accuracy and pertinency of the citeddocuments. It will be clearly understood that, although a number ofprior art publications are referred to herein, this reference does notconstitute an admission that any of these documents form part of thecommon general knowledge in the art, in New Zealand or in any othercountry.

Throughout this specification, the word “comprise”, or variationsthereof such as “comprises” or “comprising”, will be understood to implythe inclusion of a stated element, integer or step, or group of elementsintegers or steps, but not the exclusion of any other element, integeror step, or group of elements, integers or steps.

Further aspects and advantages of the present invention will becomeapparent from the ensuing description which is given by way of exampleonly.

DISCLOSURE OF THE INVENTION

According to one aspect of the present invention, there is provided aprosthesis for insertion into a joint, including

a first plate configured for fixing to a first bone forming part of thejoint,

wherein the first plate is configured to accommodate one or more of thenative ligaments in or around the joint.

According to another aspect of the present invention, there is provideda prosthesis for insertion into a patient's knee joint, including

a first plate that has a deep surface and a superficial surface,

wherein the deep surface is shaped to conform to at least a portion ofthe lateral margin or at least a portion of the medial margin of a boneforming part of the patient's knee joint.

According to another aspect of the present invention there is provided aprosthesis, including

a first lateral plate that is shaped to conform to at least a portion ofthe antero-lateral margin of the patient's femur and a second lateralplate that is shaped to conform to at least a portion of theantero-lateral margin of the patient's tibia,

a first medial plate that is shaped to conform to at least a portion ofthe antero-medial margin of the patient's femur and a second medialplate that is shaped to conform to at least a portion of theantero-medial margin of the patient's tibia,

wherein at least one of the first lateral plate or the first medialplate is configured to in-use accommodate one or more of the nativeligaments in or around the patient's knee joint.

According to another aspect of the present invention, there is provideda prosthesis for insertion into a joint, including

a first plate configured for fixing to a first bone forming part of thejoint, wherein the first plate includes an articulating surface,

a second plate configured for fixing to a second bone forming part ofthe joint, wherein the second plate includes an articulating surface,

and further wherein the respective articulating surfaces are shaped toin use cooperate with each other to guide movement of the second bonerelative to the first bone through a desired range of motion.

According to another aspect of the present invention, there is provideda method of implanting a prosthesis in a joint, including the followingsteps in any order:

-   -   (a) aligning a first plate including an articulating surface        with a first bone forming part of the joint;    -   (b) securing the first plate to the first bone;    -   (c) aligning a second plate including an articulating surface        with a second bone forming part of the joint;    -   (d) securing the second plate to the second bone;        -   wherein the method ensures that the articulating surfaces            can in use co-operate with each other to guide movement of            the second bone relative to the first bone through a desired            range of motion.

A prosthesis kit, including

-   -   (a) a first plate configured for fixing to a first bone forming        part of a joint;    -   (b) a second plate configured for fixing to a second bone        forming part of the joint;        -   wherein each of the first plate and second plate have            articulating surfaces that are shaped to co-operate with            each other when the prosthesis is fitted into the joint so            as to guide movement of the second bone relative to the            first bone through a desired range of motion.

According to another aspect of the present invention, there is provideda fastener for fixing a prosthetic structure to bone, including

a body with a length,

a first point end,

a second end distal to the first end

wherein the second end is configured to facilitate inserting thefastener into bone, and wherein

the body has a section with a generally triangular cross section.

In an embodiment, the present invention may aim to alter theetio-pathogenesis of OA, by providing a mechanism to partially bypassthe stresses experienced by a joint (articulating) surface(s). In apreferred embodiment this is achieved by sharing the load with thenative joint surface. The implant of the invention assists the joint tobear the prolonged constant high stress and excessive impulsive stressesthat are detrimental to joint physiology, while maintaining somephysiological stress to be transferred through the native joint surface.

It should be appreciated that the term “desired range of motion” refersto the preferred motion path as well as the angle of movement.

In a preferred embodiment, the desired range of motion is a functionalrange of motion for the joint.

In a particularly preferred embodiment, the joint may be guided to moveas it is physiologically designed to do so, and preferably with a fullrange of normal movement e.g. maximum extension/flexion, and/orpronation/supination.

Importantly, a prosthesis according to the present may provide a fullrange of motion of the treated joint which corresponds to the nativejoint. At the same time, the prosthesis may protect the native bonesforming the joint, while potentially providing symptomatic relief,improved joint recovery and improved function. The present prosthesiscan also be applied using a relatively smaller operation than totaljoint replacements, or in the case of a knee prosthesis the High TibialOsteotomy (HTO).

In a preferred embodiment the present invention is intended for use injoints including knees, elbows, ankles, fingers, shoulders, wrists, orhips. Various exemplary joints including embodiments will be discussedherein. However the discussion of these embodiments should not be seenas limiting and alternatives are envisaged.

Throughout the present specification reference will be made to the firstbone of a joint and the second bone of a joint. These terms should begiven their ordinary meaning as would be known to those skilled in theart. For instance, in the embodiment of a knee prosthesis the first boneis the femur while the second bone is the tibia. In a hip prosthesis thefirst bone is the pelvis while the second bone is the femur.

Certain joints may include third bones such as the radius of the elbow.

Embodiments of the present to account for such joints are discussedbelow.

Throughout the present specification the term first plate or secondplate should be understood as meaning components having a width andwhich are configured for fixing to a first or second bone.

In a preferred embodiment the first and/or second plates have a deepsurface that is shaped to conform to at least part of a surface of abone to which the plate will be attached. This may facilitate the forceplaced on the prosthesis to be distributed more evenly with respect tothe joint, rather than creating points of concentrated pressure. Theprosthesis may also be more compact and better suited for insertion intothe joint.

The first and/or second plates also have a superficial surface, which ison the distal side of the deep surface from the bone. In other words,the deep surface is the surface of a plate which is closest to the boneto which the plate is attached in use, while the superficial surface ofthe plate is the surface distal to the surface of the bone. The distancebetween the deep surface and the superficial surface defines a thicknessfor the plate(s). It should also be appreciated that the thickness ofthe plate(s) may vary.

The present invention may also include more than two plates. This willdepend on the particular joint with which a prosthesis is used. Forinstance in an elbow or shoulder joint, a third plate (and evenpotentially a fourth plate), could be secured to bones forming the jointsuch as to facilitate movement of the joint through a desired range ofmotion. In the case of an elbow joint the second plate may be secured tothe ulna and the third plate secured to the radius. Each of the platesmay have a bearing surface that cooperates with a corresponding bearingsurface on one or more plates secured to the humerus.

It is also envisaged that the prosthesis could be provided by two pairsof plates. For instance, in a knee joint, a pair of plates could befixed to the lateral margins of a knee joint (a pair of lateral plates)and a second pair of plates could be fixed to the medial margins of aknee joint (a pair of medial plates). In this embodiment, thearticulating surfaces of each pair of plates are shaped so as to conformto, and/or mimic, the shape of condyles of bones forming the knee joint.

In a preferred embodiment, the plates may be shaped and/or otherwiseconfigured to facilitate its insertion into a joint while accommodatingthe joint's native ligaments.

For instance, a plate may have an aperture or opening that extends fromthe deep surface to the superficial surface. When the plate is insertedinto a joint and positioned relative to a bone of the joint, at leastone native ligament in or around the joint can extend through theaperture.

In addition, the aperture may be unbounded at an edge which canfacilitate the plate being inserted into the joint and the ligament(s)to extend from through the aperture. This will allow the plate to betwisted around the ligament(s) before being secured in position to thenative bone.

It is also envisaged that a plate according to an embodiment of theinvention is shaped and configured to slide under and extend along aligament of a joint. For instance, a tibial plate may have a firstportion which extends along the sagittal plane (e.g. anterior toposterior) and a portion which extends along the vertically (e.g.proximate to distal). The first portion can lie underneath a/theligament, which may enable the plate to provide an articulating surfacewhile also accommodating the native ligament(s). The second portion alsoaccommodates the ligament(s) by reducing irritation or touching of thesecompletely. However, the second portion provides an increase surfacearea to attach to the tibia and therefore may facilitate better loaddistribution into the tibia at locations away from the articulatingsurfaces.

Alternatively, a plate according to the invention may be provided by twoor more components. In use, the first component of the plate ispositioned relative to the joint so that the ligament(s) is/arepositioned in an aperture in the first component. A second component ofthe plate is positioned relative to the first component, the first andsecond components are attached to the bone, such as using fastenersdescribed herein, or any other suitable fastener.

These features help to secure the plates in position without thenecessity of cutting the native ligaments. This may promote patientrehabilitation. In addition, the aperture may provide advantages such asenabling the joint to move through range of motion while minimizing orsubstantially eliminating irritation to the ligament(s).

Yet a further advantage that may be provided by the advantage is that,as the prosthesis accommodates the native ligament(s) in and around thejoint that the ligaments can continue to perform their normal functions.For instance, the ligament(s) can act to hold the bone while muscle movethe bones of the joint. That is, action of the ligament(s) is/aresubstantially unaffected by the presence of the plate(s).

In an embodiment, the first component of the plate and a secondcomponent of the plate may be connected together in vivo, such as when aprosthesis according to the invention is fitted to a patient. However,it is also envisaged that the plate sub-parts may be connected to eachprior to implantation to a patient.

In an embodiment, it is envisaged that the first plate component andsecond plate component may have features or structure to align them withrespect to each other and/or attach them together. For instance, thefirst plate component may have channel(s) and/or protrusion(s) while thesecond plate component may have channel(s)/protrusion(s), and therespective channel(s) and/or protrusion(s) engage each other.

It is also envisaged that the features or structure may prevent orrestrict movement of the components with respect to each other in onedirection only. Additional movement of the plate components in otherplanes/directions may be restricted by fasteners as described herein.

The articulating surface(s) may facilitate transferring weight or forceapplied to a joint substantially away from the native joint articulatingsurface. This may enable the plates to transfer the force to the bonessurrounding the joint. For instance, in a knee prosthesis embodiment ofthe invention, the plates may be secured to the antero-lateral and/orantero-medial margins of the native bones forming the knee joint, andtherefore interaction of the articulating surfaces assists to transferweight/force into the antero-lateral and/or antero-medial margins of thenative bones.

In addition, the articulating surfaces also facilitate the first plateand second plate, and therefore the bones forming the joint, moving withrespect to each other. This may be provided by the articulating surfaceshaving low frictional coefficients so that they can slide relative toeach other. Alternatively, ball bearings or other components may beprovided between the articulating surfaces so as to allow these to movewith respect to each other. This is useful is providing a joint with adesired range of motion.

In the preferred embodiment the articulating surfaces cooperate so as toguide the movement of the bones forming the joint with respect to eachother. This is achieved by providing at least one of the articulatingsurfaces with a shape corresponding to the desired range of motion.

In a particularly preferred embodiment, at least one of the articulatingmay have a shape corresponding to an articulating surface of a naturaljoint. For instance, an articulating surface of a knee prosthesis may beshaped so as to conform to, or mimic, the condyles of the femur. Thisarticulating surface is a complex shape, having a series of involutemidpoints generally falling on a spiral. The cooperating articulatingsurface is shaped to correspond to the condyles of the tibia.

Alternative embodiments of the articulating surfaces will be discussedin more detail below by reference to different embodiments of prosthesisaccording to the present invention.

It is also envisaged that the articulating surfaces can be shaped toprovide a desired range of motion other than that of native joint.

In yet a further embodiment, the articulating surfaces may be shaped soas to provide a range of motion for the joint corresponding to that of anative joint, yet have a shape which does not correspond to thearticulating surfaces of that native joint. For instance, in anembodiment of an ankle joint, articulating surfaces of first and secondplates define a range of motion corresponding to an arc of motion of thenative joint, yet have shapes that do not correspond to the articulatingsurfaces of the ankle joint. Accordingly, the foregoing should not beseen as limiting on the scope of the present invention.

These aspects of the present invention should become clearer from thefollowing description.

In a preferred embodiment, the prosthesis according to the presentinvention are configured to maintain separation (offloading) of thenative bones forming a joint. This may allow the articulating surfacesof the prosthesis to facilitate the desired range of motion whileminimising aggravation to those surfaces. That is, the articulatingsurfaces act as and provide, a track and guide for the bones to movewithout relying on the native joint surfaces. Note that the movement ofthe bones occurs by (or over) the articulating surfaces touching eachother, rather than the native joint surfaces. These aspects of thepresent invention should become clearer from the following discussion ofthe preferred embodiments of the present invention.

Various embodiments are envisaged for the track and guide aspects of thearticulating surfaces. For instance, articulating surfaces may bemembers and channels/grooves. Alternatively, a track may be a concavechannel having a curve within which an elongate convex articulatingsurface can move.

Alternatively, ball and socket type arrangements are envisaged.

Yet a further embodiment of a track and guide envisaged as being withinthe scope of the present invention is a recess having a shelf or lip.Such an arrangement provides an articulating surface having a shapecorresponding to the desired range of motion. A correspondingarticulating surface cooperates with the recess and shelf/lip.Accordingly, the foregoing should not be seen as limiting.

Throughout the present specification reference to the term “range ofmotion” should now be understood as meaning the distance and directionof movement of two or more bones forming a joint with respect to eachother.

In a preferred embodiment the desired range of motion is a normal rangeof motion of a joint. That range of motion will vary between differenttypes of joints according to each joints' native characteristics. Forinstance, in a knee prosthesis the present invention will allow thefemur and tibia bones to move with respect to each other through anormal range of flexion and extension. The prosthesis enables the bonesto rotate to accommodate locking of the knee at extension.

In an alternate embodiment such as an elbow joint, the prosthesis canprovide flexion and extension of the joint according to normal movementof the ulna and humerus. The prosthesis also facilitates rotationalmovement of the radius that occurs during pronation or supination of theforearm.

However the foregoing should not be seen as limiting as alternatives areenvisaged including those where the prosthesis provides a range ofmotion less than a full range for a native joint. This may be beneficialwhere joint mobility is to be restricted to account for a medicalcondition or limitations of another joint/limb.

In a preferred embodiment, the prosthesis according to the presentinvention are configured to transfer some of the stress to which thejoint is exposed into cartilage of the joint. This may be achieved bythe relative spacing or interaction of the first plate and second plate,and/or their respective articulating surfaces.

Alternatively, a deformable component may be utilised. The deformablecomponent allows movement of the first plate and second plate towardseach other. However, the deformable component maintains sufficientseparation of the native bones forming the joint such that these do nottouch each other and articulation of the joint occurs via the bearingsurfaces.

According to another aspect of the invention, there is provided aprosthesis for complete or partial insertion into the articular capsuleof a patient's knee joint. For instance, the plate(s) as describedherein may be positioned between the knee and the synovial membranewhich contain the patella, ligaments, menisci and bursae of the kneejoint. Similarly, alternate embodiment of the invention may or may notbe located within the capsule of the respective joint. In theseembodiments, the plate(s) are able to accommodate the native ligamentsof the knee joint and therefore may facilitate movement of the kneejoint as substantially described herein.

Having the component(s) of a prosthesis according to the inventioninside the capsule also facilitates use of the space in the native jointto provide the prosthesis, and therefore assist with providing a lowprofile or less obtrusive implant.

This invention may also be said broadly to consist in the parts,elements and features referred to or indicated in the specification ofthe application, individually or collectively, and any or allcombinations of any two or more said parts, elements or features, andwhere specific integers are mentioned herein which have knownequivalents in the art to which this invention relates, such knownequivalents are deemed to be incorporated herein as if individually setforth.

The invention consists in the foregoing and also envisages theconstruction and use of alternatives, of which the following givesexamples only.

BRIEF DESCRIPTION OF THE DRAWINGS

Further aspects of the present invention will become apparent from theensuing description which is given by way of example only and withreference to the accompanying drawings in which:

FIG. 1 is a back view of the prosthesis in situ, attached to a kneejoint.

FIG. 2 is a rear perspective view of the joint and prosthesis shown inFIG. 1.

FIG. 3 is a front view of the prosthesis and knee joint shown in withcross rods inserted.

FIG. 4 is a rear perspective view of the prosthesis shown without thejoint.

FIG. 5A is an exploded perspective view of a preferred embodiment of afemoral component of the prosthesis.

FIG. 5B is an exploded perspective view of an alternate embodiment of afemoral component of the prosthesis.

FIG. 6A is an exploded perspective view of a preferred embodiment of atibial component of the prosthesis.

FIG. 6B is an exploded perspective view of an alternate embodiment of atibial component of the prosthesis.

FIG. 7 is a view of a femoral component and a tibial component showingthe mounting features.

FIG. 8A is a perspective view of a fastener pin.

FIG. 8B is a perspective view of an alternate embodiment of a fastenerpin.

FIG. 9A is an anterior view of lateral and medial femoral articulatingcomponents.

FIG. 9B is a posterior view of FIG. 9A.

FIG. 9C is a perspective view of the components of FIGS. 9A and 9B.

FIG. 10 is a front view of an elbow in extension with a prosthesisaccording to the present invention.

FIG. 11 is a side view of an elbow in flexion with a prosthesisaccording to the present invention.

FIG. 12 is a side view of a finger in extension with the prosthesisaccording to the present invention.

FIG. 13 is a front view of FIG. 12.

FIG. 14 is a front view of a hip joint with a prosthesis according tothe present invention.

FIG. 15 is a partial view of a pelvis showing components of a prosthesisaccording to the present invention.

FIG. 16 is a front view of a shoulder joint including a prosthesisaccording to the present invention.

FIG. 17 is a side view of FIG. 16.

FIG. 18 is a side view of an ankle including a prosthesis according tothe present invention.

FIG. 19 is a back view of FIG. 18.

FIGS. 20A-D are side views of a knee showing representative steps infitting a prosthesis according to the present invention.

FIGS. 21A-E are medial views of a patient's left knee showing aprosthesis according to the present invention facilitating movementbetween extension and flexion.

FIGS. 22A-E are anterior views of a patient's left knee showing aprosthesis according to the present invention facilitating movementbetween extension and flexion.

FIGS. 23A-E are lateral side views of a patient's left knee showing aprosthesis according to the present invention facilitating movementbetween extension and flexion.

FIG. 24A is a side exploded view of an alternate embodiment of a femoralplate according to an embodiment of the invention.

FIG. 24B is a side view showing the femoral plate of FIG. 24A assembled.

FIG. 25A is a side exploded view of a second alternate embodiment of afemoral plate according to an embodiment of the invention.

FIG. 25B is a side view showing the femoral plate of FIG. 25A assembled.

FIG. 26A is a side exploded view of a third alternate embodiment of afemoral plate according to an embodiment of the invention.

FIG. 26B is a side view showing the femoral plate of FIG. 26A assembled.

FIG. 27 is an anterior view of a knee joint showing a knee prosthesisaccording to an embodiment of the invention and the capsule.

BEST MODES FOR CARRYING OUT THE INVENTION

The prosthesis, methods of implantation and fixation will now bedescribed in more detail with reference to the drawings. Specificdiscussion of the embodiment of the prosthesis in respect of a kneejoint is provided below. Substantively similar principles apply to thecomponents of the knee prosthesis as they do to prosthesis used in otherjoints such as the ankle, finger, elbow, or shoulder. One skilled in theart would appreciate that the discussion in respect of the kneeprosthesis is equally applicable in respect of other joints.

The present invention may be provided as a kitset of parts, includingany one or more of the components described herein. It is envisaged thata kitset for an ankle, shoulder, elbow, finger or hip prosthesis couldinclude components based on those described with reference to the kneeprosthesis.

Knee Prosthesis

Referring first to FIGS. 1 to 9C, a preferred embodiment will bedescribed in detail which utilises a pair of plates on the medial sideof the knee joint (“the medial pair of plates”) and a pair of plates onthe lateral side of the joint (“the lateral pair of plates”). However,it should be appreciated that only one side of the joint (e.g. the medalor the lateral side) could be treated with the present invention.

The lateral pair of plates includes a femoral plate 2 and a tibial plate4, while the medial pair of plates includes a femoral plate 3 and atibial plate 5. The prosthesis is provided for implantation into a kneejoint and is attached directly to the surfaces of the distal femur andproximal tibia as generally illustrated in FIGS. 1-3.

The prosthesis is a low profile structure, being widest at the joint endand becomes progressively narrower further away from joint. Theprosthesis allows space for important soft tissue structures includingligaments around the joint.

Each femoral plate 2, 3 and tibial plate 4, 5 may have a different shapeand/or configuration depending on the condoyle of the femur or tibia towhich it is to be attached i.e. each component may be configuredaccording to the anatomical specificity of the bone involved ensuring agood fit. For instance, as is shown in FIGS. 1-3:

-   -   Femoral plates 2, 3 are shaped to conform to the antero-lateral        and antero-medial distal end of the femur respectively. In        particular, the femoral plate 2 has a deep surface which        confirms to a surface of the antero-lateral distal end of the        femur, while femoral plate 3 has a deep surface which conforms        to the antero-medial distal end of the femur.    -   Tibial plates 4, 5 are shaped to conform to the antero-lateral        and antero-medial proximal end of the tibia respectively.        Accordingly, the tibial plate 2 has a deep surface which        conforms to a surface of the antero-lateral proximal end of the        tibia, while tibial plate 4 has a deep surface which conforms to        the antero-medial proximal end of the tibia.

In the embodiment illustrated in FIGS. 1-3 the femoral plate 3 wrapsaround the lateral prominence of the femur while the femoral plate 2wraps around the medial prominence of the femur.

The femoral plates 2, 3 are each generally tear drop shaped, with theanterior end being wider than posterior end in the direction of thesagittal plane. Therefore, each of the femoral plates 2, 3, wrap aroundthe antero-lateral and antero-medial margins of the respective condoyleof the femur.

The tibial plates 4, 5 are each generally “L” shaped, having a firstportion which extend generally along the transverse plane of the kneejoint, and a second portion extend generally along a sagittal planethrough the knee joint. The first portion of each tibial plates extendsposteriorly to fit underneath the medial collateral ligament and thelateral collateral ligament respectively. This is best seen in FIGS.20A-20D. As a result, the tibial plates 4, 5 accommodate the nativeligament of the knee joint.

The second portion is orientated to extend generally downwards along thelength of the tibia, and to be positioned adjacent to the medial orlateral collateral ligaments (as the case may be).

Articulating surfaces are provided on the distal margins of the femoralplates 2, 3 and on the proximal margins of the tibial plates 4, 5 toallow movement of the joint. The inner (deep) edges of the articulatingsurfaces of the femoral plates approximately follow the lateral/medialborders of the native joint articulating surfaces respectively. However,as can be seen in FIGS. 1, 2 & 3, the femoral plates 2, 3, and thetibial plates 4, 5, and/or the respective articulating surfaces, takesthe natural space available between the ligament and bone and do notsubstantially extend into the medial or lateral compartments of the kneejoint. However, the plates and/or articulating surfaces span the gapbetween the condoyles of the femur and tibia, to assist with completelyor partially separating the native articulating surfaces of the joint(if required).

As shown in FIGS. 1 and 2 (and as is discussed in more detail below) thearticulating surfaces of the plates are shaped so that they provide adesired range of motion for the native knee joint.

The articulating surfaces are broader posteriorly to accommodate therotation and sideway motion of the knee in flexion. The articulatingsurface is slightly concave to allow for the rotation and locking of theknee in extension.

Accordingly, a portion of the total load applied through the joint iscarried by the prosthesis along the medial and lateral margins of thenative joint structure.

In a preferred embodiment, articulating surfaces are provided byseparate articulating components 8A, 8B which are attached to distaledges of the femoral plates 2, 3 at or towards posterior edge. It isalso envisaged that the articulating surfaces could be formed integrallyinto the femoral plates 2, 3.

Referring to FIG. 9A which show views of an articulating component 8A ofa lateral femoral plate and an articulating component 8B of a medialfemoral plate. The articulating components 8A, 8B provide articulatingsurfaces for the femoral plates 2, 3.

In a preferred embodiment, the femoral articulating components 8A, 8Beach comprise a steel backed ultra-high density ceramic material toimprove its wear characteristics.

The articulating components 8A, 8B are attached to the femoral plates 2,3 via fasteners. A first fastener embodiment is shown in FIG. 5A. Analternate embodiment fastener system is shown in FIG. 5B in which hooks9 attach the articulating components 8A, 8B to the femoral componentsplates 2, 3.

The articulating surfaces of the articulating components 8A, 8Bpreferably have dimensions of approximately 2-3 mm thickness andapproximately 4-6 mm of width. The length of the articulating surfacescan vary so as to fit different recipients. These are likely to be inthe range of 12-18 mm.

The articulating surfaces of the invention are shaped to correspond toand/or mimic the articulating surface of the native femur bone formingpart of the knee. The articulating surfaces do not have a simplemathematical shape. Rather, they are shaped and configured to mimic thefunction of and range of motion of, the native knee joint. This isimportant in the prosthesis providing a full range of motion being ableto replace the knee joint rather than simply assist the native kneejoint's operation.

It should also be noted that the articulating surfaces of the inventionare positioned outside of the medial and lateral edges (respectively) ofcondoyles of the femur, as can be seen in FIG. 3, amongst others.Therefore, the articulating surfaces of the illustrated embodiment arenot identical to the native articulating surfaces of the condoyles.

In a preferred embodiment, a deformable component 10 is provided inbetween the articulating components and the respective femoral plates 2,3. Preferably the deformable component 10 is approximately 2-3 mm thickand is made of a bio-compatible polymer, and operates to absorb some ofthe forces applied through the joint. Preferably, the polymer has ayoung's modulus of approximately 5-20 times that of articular cartilageand is substantially impervious to creep. In a most preferred embodimentthe polymers modulus is 5-10 times that of cartilage. It is alsopreferred that the material have a Poisson ratio of approximately 0.3which is typical of cancellous bone. For example, the deformable member10 may be a synthetic carbon polymer (eg: PMMA). Preferably, thedeformable component 10 is made from a material which will allow thejoint (as a whole) to deform in a manner comparable to normal articularcartilage under the expected physiological stress. It may be preferablethat the deformable component deforms slightly less than typicalcartilage in order to increase the proportion of the load transferred bythe prosthesis.

Other materials suitable for the deformable component are Ultra HighMolecular Weight Polyethylene (UHMWPE); silicone polycarbonate urethane;or rotaxane.

The deformable component 10, provides a deformable structure between thecomparatively rigid femoral component 2, and corresponding tibialcomponent 4, and bone. The component 10 is preferably held in placebetween the articulating component 8A or 8B and femoral plate 2.

The deformable component may be mated with the articulating component 8Aor 8B and the respective femoral plate 2 or 3.

For instance, in the embodiment shown in FIG. 5A the femoral plates 2, 3may include a groove 17 which receives a corresponding projection or ribof the deformable component 10. Similar grooves and projections may beprovided at the interface between the component 10 and the articulatingcomponent 8A or 8B.

In one embodiment, the tibial plates are approximately 2-3 mm thick andapproximately 4-6 mm wide.

Tibial articulating surfaces are provided on proximal margin of thetibial plates 4, 5. As shown in FIG. 3 amongst others, the articulatingsurfaces of the tibial plates 4, 5 are located outside of the lateralmargins of the condoyles of the femur and tibia. Therefore, thearticulating surfaces of the illustrated embodiment are not identical tothe native articulating surfaces of the condoyles.

The tibial articulating surfaces are preferably shaped so as tocorrespond to and/or mimic approximately the middle two thirds of themedial/lateral border of the native knee joint articulating surface.

In one preferred embodiment, a separate articulating component may besecured to each of the tibial components 4, 5. Each articulatingcomponent has a shape that corresponds to the articulating surface ofthe native condoyles of the tibia. The articulating components arepreferably a ceramic material secured to a metallic base. The ceramicmaterial has a low coefficient of friction, therefore allowing thearticulating surfaces of the femoral and tibial components to slideacross each other with low or minimal resistance.

An alternative embodiment of an articulating surface is shown in FIG.6B, where the articulating components 8A, 8B each include a plurality ofball bearings 14. Each ball bearing 14 is approximately 2 mm in diameterand made from ceramic coated stainless steel. There may be approximately5 to 10 ball bearings 14, and the corresponding bearing housing may alsobe coated with a ceramic material to improve the wear characteristics ofthe interface. Alternatively, the tibial articulating components 8A, 8Bmay be a polished metal or ceramic surface.

The articulating components 8A, 8B act as an articulating surface thatin use interacts with the corresponding articulating component on afemoral plate 2, 3, to provide a range of motion for the joint.

The articulating components 8A, 8B can be secured to the tibialcomponent using several fastener arrangements. For instance, oneparticularly preferred embodiment is shown in FIG. 6A, where a latch 11mates with a corresponding groove (not shown) on tibial component 4, 5to secure these together.

An alternate securing system is shown in FIG. 6B. A number of hooks 12engage with apertures in tibial plate 4, 5.

A deformable component 13 may be provided between the articulatingcomponents, and the tibial plate 4, 5. The deformable component 13 isapproximately 2-3 mm thick. To secure the deformable component 13,between the articulating components and the tibial components, theunderside of articulating component 11 may have a longitudinal groove(shown in FIG. 7) for receiving and mating with the deformable component13. Similarly, the deformable component may have a rib or projection onthe underside for a corresponding groove 18 in the proximal edge of thetibial plates 4, 5.

In their preferred forms, the femoral plates 2, 3 and tibial plates 4, 5are made from a non-bioactive material that is stiff and hard such asstainless steel or titanium. In a most preferred form, titanium is used.It is also preferred that both the femoral and tibial plates include anumber of apertures or holes 20. This reduces the bulk of the metalwithout significantly compromising its stress distributing properties.The holes may also allow soft tissue attachment and hence the nutritionof the bone thereby not disturbing normal biology significantly.

The superficial surface of the femoral and tibial plates 2-5 arepreferably polished to minimize rubbing of the surrounding soft tissueswhich may result in irritation. The deep surfaces are also smooth, butmay include multiple protrusions (not shown) to keep the componentdistanced from the bone surface. For example, a number of spacedprotrusions approximately 1 mm long may project from the deep surfaces,to separate the plates from the bone, in order to reduce the risk ofpressure necrosis of the bone commonly seen after plating of fracturedbone.

The prosthesis according to the present invention is a stress sharingdevice suitable for minimally invasive, surgical implantation around theknee joint without compromising the native joint surface. Accordingly,it substantively transfers potentially damaging stress from the jointand distributes this to the tibia and femur bones at locations away fromthe joint. This allows the joint to repair itself by maintaining thebasic physiological strain at the joint surface. In extreme cases theprosthesis could take substantially all the stress from the joint. Thearticulating surfaces facilitate the joint having a desired range ofmotion.

The present invention may also find application as a stabilisationmethod for treatment of intra-articular fractures.

Multi-Component Plates

Referring now to FIG. 5A. The femoral plate 2 may be provided by a firstcomponent 100 and a second component 102. The first component 100 has anaperture 104 which extends from the deep surface to the superficialsurface of the femoral plate 2. The aperture 104 is open at an edge 106to the perimeter 108 of the plate 2, which defines a channel indicatedas 110. The channel 110 includes a generally square shaped sub-channel112, a generally triangular shaped sub-channel 114, and a generallysquare shaped protrusion 116.

The second component 102 has a shape corresponding to the shape of thechannel 110. In addition, the second component 102 has structure 118,120, 122 configured to engage with the structure 112, 114, 116 in thefirst component 100.

The aperture 104 has a generally oval shape and is configured to receivethe deep medial collateral ligament 150 and the medial collateralligament 152, as can be seen in FIGS. 20D and 23A-D.

While not shown in FIG. 5A, the femoral plate 3, has a similar two-partstructure to the femoral plate 2.

Provision of an aperture in a plate 2 or 3 of the invention mayfacilitate provision of a knee implant with minimal damage, irritationor disturbance to the native soft tissue of the joint. For instance, theaperture enables the plate(s) to accommodate the native ligaments. Theprosthesis according to the invention can also therefore use the nativeligaments to achieve movement of the bones of the joint.

Fastening Methods

In one preferred form, the tibial and femoral plates 2-5, have multipletriangular holes 19 to accommodate corresponding bone fasteners 15.Preferably, the flat portion of the triangle shaped holes 19 is orientedto be perpendicular to the line of stress through the joint, to improvetransmission of stress from the prosthesis to the bone. That is, thepoints of the triangle are oriented to point towards the respectivejoint surface. As best shown in FIG. 3, the triangle points facedownwards for the femoral plates 2, 3, and triangle points face upwardsfor the tibial plates 4, 5.

The bone fastener pins 15 are designed to transmit the stress from thefemoral and tibial plates to the corresponding bony structures to whichthey are attached. The fastener 15 is hammered into the bone through theapertures 19 in the femoral and tibial plates.

One embodiment of a fastener is shown in FIG. 8A. One end of thefastener 15 includes a head 21, having a triangular cross section. Thehead 21 narrows through body section 22 to point 23. End 21 has anengagement point 22 and a plurality of barbs 16 extend from bodysection.

In use, fastener pins 15 are inserted through holes 19 in the plates 2-5further than required. Engagement point 22 is used to draw the fastenerpin 15 backwards towards femoral and tibial plates 2-5. This assists inbarbs 16 engaging the cancellous bone so as to secure the fastener pins15, and thereby the plates 2-5, in position.

An alternate embodiment of the fastener pin is shown in FIG. 8B. End 21has a thin sheet of elastic metal 24 attached at the center. Elasticmetal sheet 24 is larger in size as compared to end 21. Duringinsertion, end 21 should be pushed in further to preload the fastenerspins in their inserted position. This will create elastic recoil andhelp to fix the barb end in the cancellous bone. The point end 23,preferably includes a barb 16 for fixation in the cancellous bone. Inits preferred form, the barb 16 is approximately 5 mm in length.

The bone fastener may be made from stainless steel, or most preferably,titanium.

The medial and lateral femoral plates 2, 3 may also be fixed with anumber of locking rods 22 as shown in FIGS. 3 & 4. These four lockingrods 22 pass through the corresponding bone are fix the pair of femoralplates and tibial plates together respectively. The plates 2-5 also haveholes for the attachment of the cross rods 22. In order to insert therods 22, a hole is drilled in the bone to accommodate the rods. A guideis used to direct the drill hole between the corresponding holes 25 inthe femoral/tibial plate. The required length of the rods 22 aremeasured by the guide. A ball tipped rod 22 is inserted from one side,while the other end of the rod 22 is threaded. A nut is applied to thethreaded end, and tightened to achieve the required strain. The excessthread can then be cut flush.

Alternatively, it is envisaged that conventional screwing techniquescould also be used to fix the prosthesis to the bony structures.

Implantation Method

A method is provided for implantation of the prosthesis according to thepresent invention. The method will be described herein with reference toinsertion of the knee joint. However this should not be seen as limitingand it should be appreciated that similar steps are involved inimplanting prosthesis to other joints. One skilled in the art should beable to extrapolate from the steps described herein so as to work thepresent invention.

Before implanting the prosthesis, the patient's knee joint may beexamined by a non-invasive imaging procedure such that appropriatelysized and shaped components may be selected. A variety of non-invasiveimaging devices may be suitable, for example CT scan, or X-ray devicesand the like. Two methods of non-invasive imaging for selection of asuitable prosthesis are preferred.

In the first method, CT scan or other non-invasive imaging scans,optionally coupled with exterior measurements of the dimensions of therelevant proximal tibia and proximal femur bone, may be used toestablish a library of prostheses whose size and geometry differaccording size of the patient. A limited number of “standard” prosthesesare then made to meet the requirements of a generic population ofpatients. In this first method, a non-invasive imaging scan, such as anX-ray or CT scan, together with clinical measurement will enable thesurgeon to select a prosthesis of the best size and shape from thelibrary for a particular patient. With this method, it is expected thatsome modification of the patient's bony structure may be necessary.However, an extensive set of standard sizes can be created to minimizethe modification required to the joint's anatomy.

In a second method, each patient receives one or more prostheses thatare custom tailored for the individual. Such a prosthesis may beconstructed from imaging data (i.e., X-ray or CT scan data) by asuitable computer program. The second method is likely to result in animproved fit to a patient's unique anatomy, and/or reduce the need toshape the exterior surfaces of the patient's bones.

Surgery can be done under general or local anesthesia. The patient ispositioned supine with a radiolucent wedge located underneath the knee,and the operation is done under tourniquet control and image intensifierguidance. An antero-lateral and posteromedial approach to the distalfemur and proximal tibia is utilized to approach the distal femur andproximal femur. All the soft tissue is taken off from the bone as a softtissue sleeve.

Insertion of the prosthesis of the present invention is typically donevia a 10 cm to 14 cm length incision to the capsule on the medial andlateral margins of the joint. The articulating body of the femoralcomponent is aligned with the lateral/medial edge of joint surface. Itsposition is checked visually and radiological using intra-operativeX-ray. Once acceptable alignment is achieved, it is temporarily fixedwith the help of wires. A set of standard size templates may be providedduring the surgery to achieve initial alignment and appropriate sizing.Once an exact size is determined the prosthesis is applied using theinitial temporary wires. All other components of the prosthesis areattached on this base line.

The tibial component engages with femoral articulating body and it canbe preloaded depending on the clinical requirement. A pre-compression ofthe polymer insert 10 can function to take the resting stress from thejoint surface.

The next step of implantation is to align an appropriately sizedarticulating body of the femur with the joint surface and thelateral/medial edge of the femoral condyle. The implant shouldcorrespond to the condylar line in a lateral knee X-ray. Next, thetibial articulating body is placed opposing the femoral plate. Bothplates are temporarily fixed with K-wires. The appropriate position andsize can be checked using an image intensifier and an AP view is takento check the joint space. A pre-stress device can be used to pre-stressthe implant according to clinical requirement by compressing thedeformable component. Once in the correct position, rods 22 are used tofix the plates, and the triangular fasteners are hammered into the bone.The temporary K-wires are then removed. The joint can then be tested andtaken through the full range of motion.

Referring now to FIGS. 20A-D which show a medial side view of the stepsof positioning a femoral plate 2 relative to the condoyle of the femur.The steps generally form part of the method of implanting the prosthesisas described above and may therefore be used in combination with thesame, or in combination with other steps/methods.

An incision is made to the layers of the capsule as noted above. Theligament(s) of the joint are separated from the membrane forming theouter layer of the capsule.

The first component 100 is inserted through the insertion and positionedadjacent the medial condoyle of the femur. A perimeter side of femoralplate 2 is slid under the medial collateral ligament 152 and the deepmedial collateral ligament 152 so that these ligaments are positioned inthe channel 110.

The first component 100 is rotated so that the ligaments are moved intothe aperture 110 to the position shown in FIG. 20B. Rotation of thefirst component 100 continues until it reaches the position shown inFIG. 20C.

The second component 102 is positioned relative to the first component100 and inserted into the channel 110 as is shown in FIG. 20D. Thestructures on the first and second components 100, 102 engage eachother.

A similar process can be used to position the deep lateral collateralligament (not shown in FIGS. 20A-20D) and lateral collateral ligament132 in a corresponding aperture 130 in femoral plate 3, to assume theposition shown in FIGS. 23A-E.

The components of a prosthesis of the invention are located inside thecapsule, and therefore the invention provides an inter-joint prosthesis.FIG. 27 shows the location of the prosthesis relative to the native kneejoint and in particular the capsule 160. As can been seen, the ligaments132, 150 have been separated from the outer membrane forming part of theknee joint and the plates 2, 3, 4, 5 are positioned to accommodate theligaments 132, 150.

Alternative Plate Configurations

Referring now to FIGS. 24 to 26 which show alternative embodiments for atwo part femoral plate 2 or 3 according to an aspect of the invention.The embodiments of FIGS. 24 to 26 differ in the shapes of the respectivecomponents from which they are formed as illustrated.

FIGS. 24A and 24B show that the first component 200 and the secondcomponent 204 together provide a generally tear shaped femoral platehaving an aperture 206 to in use accommodate the native ligaments in theknee.

An articulating surface 208 is provided on the first component 200, andis configured to in use cooperate with a corresponding articulatingsurface on a tibial plate.

FIGS. 25A and 25B show a first component 210 and a second component 212.A first articulating surface 214 and a second articulating 216 surfaceare provided on the first component 210 and the second componentrespectively. In use, the first and second articulating surfaces 214,216 together provide an articulating surface for the femoral plate.

Together the first component 218 and the second component 220 define anaperture 225 to in use accommodate the native ligaments in the knee.

Similarly, FIGS. 26A and 26B show a first component 218 and a secondcomponent 220. The entire articulating surface (224) is provided on thefirst component 218 in FIG. 26A.

While the embodiments of FIGS. 24 to 26 all include a generally ovalshaped aperture, this should not be seen as limiting. For instance, theaperture may be round or spiral shaped, or have any other appropriateshape. In addition, while the shape of the combined first and secondcomponents is generally tear shaped, other shapes are also envisaged.

Range of Motion

Referring now to FIGS. 21A to 21E, 22A to 22E and 23A to 23E.

The pair of medial plates cooperate with each other and the pair oflateral plates cooperate with each other, to guide the bones of the kneejoint through a desired range of motion. As can be seen, the nativeligaments are accommodated by the plates as they can extend through theapertures therein. This enables the native ligaments to hold the bonesof the joint (and therefore the plates attached thereto) together.Muscles can therefore move the knee joint. Because the platesaccommodate the native ligaments the function of the native knee jointis substantially unaffected by the prosthesis. In addition, the shapeand configuration (as described above) reduces irritation or adverseeffects of the plates on the ligaments of the joint.

In addition, the articulating surfaces of the plates provide a desiredrange of motion such as a required functional range of motion or a rangeof motion otherwise corresponding to the range of motion of the nativeknee joint.

Elbow Prosthesis

Referring now to FIGS. 10 and 11 showing an elbow having a prosthesisaccording to the present invention in extension and flexion.

A first plate 26 is secured to distal end of humerus 27. The first platehas a generally “Y” shape with first arm 26A and second arm 26B. Thearms diverge so as to surround the condyle of humerus 27.

A protrusion 26C provides an articulating surface between first plate 26and third plate. A second plate 28 is secured to proximal end of ulna 29and a third plate 30 is secured to proximal end of radius 31.

Arm 26B provides a articulating surface that cooperates with bearingsurface on second plate (indicated generally as X) so as to facilitatethe ulna moving with respect to the humerus and to provide for flexionand extension of the elbow joint. This is achieved by the articulatingsurfaces being shaped so as to correspond to and/or mimic thearticulating surfaces of a native elbow joint responsible for flexionand extension.

Protrusion 26C acts as another articulating surface by slidinglycooperating with groove 30B in the third plate. The protrusion 26C canslide across arm 26A. This provides rotational motion of the radius withrespect to the humerus. That is, cooperation between articulatingsurfaces on the first and third plates facilitates pronation andsupination of the radius 31.

As can be seen in the FIGS. 10 and 11, the first plate, second plate andthird plate accommodate the native ligaments of the elbow joint, beingthe lateral collateral ligament 31B and the medial collateral ligament31C. Accordingly, the ligaments 31B, 31C can hold the joints of the bonein position as in an untreated joint.

Ankle Prosthesis

Referring now to FIGS. 18 and 19 which show an ankle prosthesis isconfigured to replicate motion of the native ankle joint. Theconfiguration of the prosthesis is designed to enable insertion into therestricted space of the ankle joint. This is necessary as theconfiguration of a foot and ankle joint means that there is little roomto secure components of the prosthesis.

A first plate 32 having an articulating surface 33 is secured tocalcaneum bone 34 on the lateral/medial edge of a foot. Articulatingsurface 33 has a generally concave shape when viewed from the lateraledge of the foot.

A second plate 35 has first arm 36 and second arm 37. The arms 36, 37diverge so as to be able to surround front and back edges of tibia 38.The arms provide articulating surfaces 39 which are generally convex inshape when viewed from the lateral edge of the foot.

Articulating surfaces 33, 39 are arcs of a circle. Therefore, thearticulating surfaces define a range of motion similar to the nativeankle joint. However, bearing surfaces 33, 39 are not shaped tocorrespond to the native ankle joint articulating surface.

Articulating surface 33 is slightly wider laterally than articulatingsurface 39. This allows for the lateral movement of the foot.

As can be seen in the FIGS. 18 and 19, the first plate and second plateand third plate accommodate the native ligaments of the ankle joint,being the lateral collateral ligament 33B and the medial collateralligament 313. Accordingly, the ligaments 33B, 33C can hold the joints ofthe bone in position as in an untreated joint.

Finger Prosthesis

Referring now to FIGS. 12 and 13 that show a finger prosthesis accordingto the present invention.

A first plate 40 is attached to a distal portion of a bone forming partof a joint, and a second plate 41 is attached to a proximal part of abone forming part of the joint. The first and second plates 40, 41 havebearing surfaces (indicated generally by Y) that cooperate to guide thesecond bone through a desired range of motion.

It is possible to have pairs of plates on distal sides of a joint as canbe seen in FIG. 13.

The shape and configuration of the plates and their respectivearticulating surfaces will vary according to the finger joint withinwhich the prosthesis is used. For instance, different shapes and rangesof motion are needed in a finger joint between a metacarpal and aproximal phalanges, compared to a finger joint between proximal phalanxand middle phalanx.

As with other embodiments, the prosthesis guides the bones forming thejoint through a range of motion and acts as a surface for that motion tooccur.

Deformable components may or may not be used with a prosthesis for afinger joint as these do not experience the same stresses as do loadbearing joints such as the knee or ankle.

As can be seen in the FIGS. 10 and 11, the first plate, second plate andthird plate accommodate the native ligaments of the elbow joint, beingthe lateral collateral ligament 31B and the medial collateral ligament31C. Accordingly, the ligaments 31B, 31C can hold the joints of the bonein position as in an untreated joint.

Hip Prosthesis

Referring now to FIGS. 14 and 15 which show a hip prosthesis accordingto an embodiment of the invention. The hip prosthesis includes a firstplate 42 secured to pelvis 43 near acetabulum 43A. First plate 42 has anarticulating surface in the form of a socket having a curve. The sockethas a lip which extends away from the pelvis so as to define a cavity toreceive a corresponding articulating surface 45.

A second plate 44 is secured to proximal end of femur. Second plate hasan articulating surface 45 with the same curvature as that of firstplate's articulating surface 46. However articulating surface 45 issmaller than articulating surface 46. This will allow articulatingsurfaces 45, 46 to move with respect to each other, and thereforeprovide a range of motion for the hip joint.

Articulating surface 46 extends over the edge between the native femurand acetabulum so as to engage with articulating surface 45.

The radius of curvature of the articulating surfaces 45, 46 is greaterthan the radius of curvature of the articulating surfaces in the nativehip joint. This may assist in keeping the native joints separated fromeach other.

The articulating surfaces 45, 46 guide the femur bone and facilitatethis moving with respect to the hip joint. The components maintainseparation between the bones of the hip joint and provide a surface forrelative movement of these.

A deformable component (not visible) can be used between the first andsecond plates. This allows forces applied to the joint to be transferredinto the cartilage of the joint. However the deformable component isconfigured to maintain separation of the hip bones, so that movement ofthe femur with respect to the pelvis occurs via the bearing surfaces.

As can be seen in the FIGS. 14 and 15, the first plate and the secondplate accommodate the native ligaments of the hip joint, being theilliofemoral ligament 47B and the pubofemoral ligament 47C. Accordingly,the ligaments 47B, 47C can hold the joints of the bone in position as inan untreated joint.

Shoulder Prosthesis

A shoulder prosthesis according to the present invention is shown inFIGS. 16 and 17. A first plate is attached to the top of scapula at thelateral margin. The first plate provides an articulating surface in theform of a recess. A lip extends back over recess to provide a cavityhaving a curvature. However, the radius of curvature of the firstplate's articulating surface is slightly greater than the radius of thenative glenoid fossa.

A second plate 48 is attached to proximal end of humerus. The secondplate provides an articulating surface which extends up and over the topof outside edge of humerus condyle. The second plate's articulatingsurface has the same radius of curvature as the first plate'sarticulating surface but is smaller. This allows the second plate'sarticulating surface to move with respect to the first plate.

The articulating surfaces cooperate so as to provide a desired angle ofmotion for the prosthesis.

The radius of curvature of the articulating surfaces is slightly greaterthan the radius of curvature of the articulating surfaces of the nativeshoulder joint. This pushes the humerus out laterally with respect tothe scapula so as to ensure that the motion of the joint occurs on thearticulating surfaces, rather than the articulating surfaces of thenative joint. This may assist in keeping the native joints separatedfrom each other.

While embodiments of the invention have been illustrated and described,it is not intended that these embodiments illustrate and describe allpossible forms of the invention. The words used in the specification arewords of description rather than limitation, and it is understood thatvarious changes may be made without departing from the spirit and scopeof the invention.

Aspects of the present invention have been described by way of exampleonly and it should be appreciated that modifications and additions maybe made thereto without departing from the scope thereof as defined inthe appended claims.

1-13. (canceled)
 14. A knee prosthesis for insertion into a patient'sknee joint, including a first plate configured for fixing to thepatient's femur forming part of the knee joint, a first bearing surfaceassociated with the first plate, wherein the first bearing surface is ashape having a series of involute mid points falling on a spiral so thatthe first bearing surface is shaped to conform to the articulatingsurface of the condoyles of the femur, a second plate configured forfixing to the patient's tibia forming part of the knee joint, a secondbearing surface associated with the second plate, wherein the secondbearing surface is shaped to conform to the articulating surface of thecondoyles of the tibia, and wherein the shapes of the bearing surfacesensure that in-use the bearing surfaces cooperate with each other toguide the movement of the patient's tibia relative to the patient'sfemur through a desired range of motion corresponding to the patient'snative knee joint.
 15. A prosthesis as claimed in claim 14, wherein apair of first plates are fixed on the lateral and medial margins of thefemur respectively, and a pair of second plates are fixed on the lateraland medial margins of the tibia respectively.
 16. A prosthesis asclaimed in claim 14, wherein the bearing surfaces cooperates to providelateral movement and axial rotation of the knee joint.
 17. A prosthesisas claimed in claim 14, including a deformable component configured totransfer a portion of force applied through the joint into cartilage inthe joint.
 18. A prosthesis as claimed in claim 17, wherein thedeformable component has material properties such that it deforms lessthan or equal to the joints native cartilage.
 19. A prosthesis asclaimed in claim 14, wherein the first and second plates include aplurality of apertures.
 20. A prosthesis as claimed in claim 19, whereinat least some of the apertures are generally triangular in shape andeach have a point.
 21. A prosthesis as claimed in claim 20, wherein thepoint of the triangular apertures are aligned to face toward the jointsurface.
 22. A prosthesis as claimed in claim 14, wherein a plurality offastening rods extend across the joint between each of said firstplates.
 23. The prosthesis as claimed in claim 14, wherein the firstplate is shaped and configured to be attached to the anteromedial and/oranterodistal ends of femur.
 24. The prosthesis as claimed in claim 14,wherein the second plate is shaped and configured to be attached to theanteromedial and/or anterodistal ends of the tibia.
 25. The prosthesisas claimed in claim 14, wherein the bearing surfaces of the first plateare shaped to follow the lateral and/or medial borders of the nativeknee joint.
 26. The prosthesis as claimed in claim 14, wherein the firstplate and the second plate are shaped so that they do not extend into agap between the condoyles of the femur and the tibia which is bounded bythe lateral and medial edges of the condoyles of the femur and thetibia.
 27. The prosthesis as claimed in claim 14, where the secondbearing surface is shaped to correspond to the middle two thirds of thelateral border of articulating surfaces of the knee joint.
 28. Theprosthesis as claimed in claim 14, wherein the first plate and thesecond plate are configured to in-use substantively transfer stress fromthe joint and distribute the force to the tibia and femur at locationsaway from the knee joint.
 29. The prosthesis as claimed in claim 28,wherein the first place has a surface that is shaped to confirm to alateral or medial surface of the condoyle of the femur.
 30. Theprosthesis as claimed in claim 14, wherein the second plate has asurface that is shaped to confirm to a lateral or medial surface of thecondoyle of the tibia.
 31. The prosthesis as claimed in claim 14,wherein the bearing surfaces of the first plate and the second plate areshaped to accommodate locking of the knee at extension.
 32. Theprosthesis as claimed in claim 14, wherein the bearing surfaces of thefirst plate and the second plate are broader posteriorly to accommodaterotation and sideway motion of the knee in flexion.
 33. The prosthesisas claimed in claim 14, wherein the bearing surface of the first plateincludes a region having slightly concave shape to allow for therotation and locking of the knee in extension.
 34. The prosthesis asclaimed in claim 14, wherein the bearing surface of the first plate hasa length in the range of 12-18 mm.
 35. The prosthesis as claimed inclaim 14, wherein the first plate has a side edge and a notch whichextends inwardly from the side edge of the plate.
 36. The prosthesis asclaimed in claim 14 including a component configured having a shapecorresponding to the junction between the side edge of the femoral plateand the notch.
 37. The prosthesis as claimed in claim 36, wherein thecomponent and the femoral component are configured to interlock to eachother.